Hydraulic fracturing is a stimulation process for creating high-conductivity communication with a large area of a subterranean formation. The process increases the effective wellbore area within the formation so that entrapped oil or gas production can be accelerated. The efficiency of the process is often measured by the total amount of contacted surface area that results from the stimulation treatment.
During hydraulic fracturing, a fracturing fluid is pumped at pressures exceeding the fracture pressure of the targeted reservoir rock in order to create or enlarge fractures within the subterranean formation penetrated by the wellbore. Once the fracture is initiated, subsequent stages of fluid containing chemical agents, as well as proppants, are pumped into the created fracture. The fracture generally continues to grow during pumping and the proppants remain in the fracture in the form of a permeable pack that serves to prop the fracture open. Once the treatment is completed, the fracture closes onto the proppants. The proppants keep the created fracture open, providing a highly conductive pathway for hydrocarbons and/or other formation fluids to flow into the wellbore.
Once the fractures have been created or enlarged, the fracturing fluids can be broken down to minimal viscosity and allowed to flow back before production. The timing of breaking can be important for practical concerns. A subtle balance often has to be struck between the initial viscosity and final viscosity after breaking. If the fracturing fluids break too early, the proppant can separate from the fracturing fluids and settle to the bottom of the fracture before a fracturing treatment is completed. In this situation, the geometry of the fracture and well productivity can be impaired.
Viscoelastic surfactant (VES) based fluids have been widely used in hydraulic fracturing, gravel-packing, and frac-packing applications for more than a decade because the fluids exhibit excellent rheological properties and maintain low damage characteristics for formation and fractures. Although the viscosity of VES fluids may be reduced by contact with hydrocarbons or dilution by formation water, to recover VES based fluids efficiently in a commercial setting, a breaker can be used to break the VES fluids to shorten the time required to clean up a well and to increase early oil/gas production.
Various breakers have been disclosed in the art. Despite all the advances, there remains a need in the art for additional materials that can effectively break VES fluids in a controlled manner.